Phase change materials are known in the art and include compounds formed from germanium (Ge), antimony (Sb), and tellurium (Te), which are known as GST materials. The phase change material is capable of being reversibly electrically switched between an amorphous state and a crystalline state. The phase change material is electrically writable and erasable and has been used in electronic memory applications. When the GST material is in the amorphous state, it is said to be “reset,” while the GST material is said to be “set” in the crystalline state. GST materials have been used in phase change random access memory (“PCRAM”) devices to provide non-volatile memory with long data retention. PCRAM devices rely on the electrically bistable status of resistance differences between the amorphous and crystalline states of the GST material.
One GST material used in PCRAM devices is Ge2Sb2Te5. However, during operation of the PCRAM device, changes in the stoichiometry of the GST material have been observed. In other words, the GST material, as deposited, includes different relative amounts of Ge, Sb, and Te than the GST material after operation of the PCRAM device. In addition, the stoichiometry of the Ge, Sb, and Te has been reported to change in an active region or contact region of the PCRAM device after repeated operation. While the relative amount of Ge in the Ge2Sb2Te5 in the active region remained constant, the Ge2Sb2Te5 became Sb-rich and Te-deficient. However, regions of the Ge2Sb2Te5 not subject to the switching maintained their original stoichiometry.
It would be desirable to form a phase change material having a desired stoichiometry, where the stoichiometry differs from that of a deposition target used to form the phase change material.